Horizontal underground boring has become a popular and cost effective method for installing gas piping and other underground utilities. In such systems, a bore head or drill bit on the end of a rotating pipe stem is pushed forward through the soil by the boring machine. Typically, horizontal boring machines use drill stems in lengths of ten or twenty feet, which are added to the end of the stem as the bore head penetration continues.
Prior to the initiation of horizontal boring, it is necessary to locate electric lines, water lines, sewer lines, and other pipes in the path of the boring machine, to avoid penetrating or damaging such pipes. A first step in this process is to obtain maps of the area in which the horizontal boring is to be made, to ascertain the location of pre-existing pipes. Frequently, however, such maps are incomplete or inaccurate. All metal pipes in the path of a boring machine may be accurately located with standard electromagnetic pipe locators. Similarly, plastic pipes with tracer wires also can be accurately located. Plastic pipes without tracer wires, however, or with broken tracer wires, and other non-conductive pipes cannot easily be located. Sewer lines typically are made of clay or orangeburg pipe, or of plastic pipe, which makes such lines difficult to locate.
Systems have been developed for detecting underground sewer lines or water lines, where the pipe for such lines is not made of metal or plastic pipe with tracer wires in it. One such system for detecting the location of an underground portion of a sewer line is disclosed in Ziska U.S. Pat. No. 4,911,012. In this patent, a sound source is provided to introduce sound of a predetermined frequency into an accessible (above ground) portion of the sewer line. The sound vibration then propagates into the underground portion of the line. The location of the underground portion of the sewer line is identified by sensing the vibration through a detector located at the ground surface or inserted into the ground above the underground portion of the sewer line. A number of different locations of the detector are made in-order to "zero in" on the underground line. This system requires considerable effort; and while it is capable of tracing the path of the underground line, it is not capable of determining the depth of that line.
The Heitman U.S. Pat. No. 5,036,497 is directed to a method and apparatus for detecting the location of an underground water line. In this system, a pulsing valve is placed on the water line to cause the water intermittently to flow and to be shut off. The result is a water hammer effect in the water line to send shock waves outward from the pipe. Spaced seismic sensors are employed to provide a differential indication of the signals; and movement of the sensors to a point where the signals received by the two sensors is equal, along a spaced path, is used to trace the path of the water line. As with the system of the Ziska patent, this is a tedious and time consuming process. It also requires the insertion of the pulsing valve in order to produce the hammer effect needed to produce the seismic signals.
The Huebler U.S. Pat. No. 5,127,267 employs a system similar to that of the Ziska patent mentioned above. In the system of Huebler, an audio speaker is used to inject an audio signal into an underground pipe from an accessible above ground input. The location of the pipe then is detected by a plurality of detectors positioned at varying distances from the pipe. These detectors generate signals, which are supplied to a signal processor. The time of arrival of the acoustic signal to the various detectors then is processed to determine the detector which is located nearest the concealed pipe. This position is marked, the detectors are moved; and the test is repeated to plot or map the direction of the pipe underground. As with the systems of Heitman and Ziska above, the depth of the pipe is not ascertained by the system of Huebler.
The Alspaugh U.S. Pat. No. 2,620,386 is directed to an earth strata cutting indicator. The system of this patent is used in conjunction with a horizontal boring machine for mining coal. For such a machine, it is important to keep the machine in a layer of coal and out of adjacent strata of rock, if possible, by remote control. To determine this, sensors are provided on the bore head for transmitting signals back to an oscilloscope. The vibrations of the bore head when it is cutting through coal differ from vibrations caused when it is cutting rock strata. These vibration differences are visibly indicated on the oscilloscope; and a synchronizing system is provided between the cutting head and the indicator to provide indicia of the circular motion of the scanning tube as the bore head cuts the strata face. Thus, the precise position of the change in strata can be determined. This then permits the operator of the machine to guide it by manipulation to cut into the desired layer of coal, and to avoid rock formations.
The Jackle U.S. Pat. No. 4,457,163 utilizes acoustical (microphone) technology for detecting a broken below-grade pipe. In this system, the emission noise generated by a leak is picked up by a microphone and an amplifier, which controls a peak noise indicator. Different measuring points detected by the amplifier are supplied to a digital memory for displaying a histogram showing noise distribution along the pipe. This information then is employed to locate the leak in the pipe.
The systems of the prior art noted above and known to applicant, however, do not provide an indication to the operator of a horizontal boring machine of the penetration of the bore head or drilling bit into a sewer pipe. Consequently, it is desirable to provide a system and method for providing such an indication to the operators of a horizontal boring machine.